Reduction of nitro and other compounds



Patented Aug. 6, 1935 REDUCTION OF Nrrno AND OTHER COMPO UNDS Henry DreyfugLondon, England No Drawing. Application October 17, 1932, Serial No. 638,178. Inqreat Britain October 22, 1931 8 Claims. (o1. 2ec e9 This invention relates to the, production of organic compounds and more particularlyto the production of hydrazobenzene and other reduction products of nitro compounds. A number ,of methods for the production of hydrazobenzene' are known, those employed von 2.

commercial scale involving the reduction of nitrobenzene, azoxyorazobenzene. Hydrazobenzone is an important intermediate product in the production'of benzidine into which it is converted by'treatmentwith acid.

" The reducing agent whichis perhaps the most commonly employed in the production of hydra zobenzene by reduction of nitrobenzene is zinc'in the presence of alkali. Where zincis employed, however, anumber of unfavourable factors have to be taken into account. For example zinc is relatively expensive. Furthermore, the reaction may not only be so violent as to get out of hand, but aniline may also be formed. Alcohol is usually employed to'diminish the production of an iline, but its use adds considerably to the expenseof the process. Where iron 'borings have been substituted for zinc in the reduction of nitrobenzene tojhydrazob enzene it has been found that other disadvantages occur. Thus a quantity of iron very considerably greater than that theoretically required to bring about complete reduction to hydrazobenzene is required in practice. It has now been found that reduction is speeded up, and quantities of iron much closer to the quantitiesascalculated may be employed for the reduction of nitro compounds to hydrazobenzene and for other reductions, especially reductions effected in neutral or alkaline media, if the iron employed as reducing agent is in a very finely divided condition, and especially if pyrophoric iron is employed.

It appears that the efficacy of the finely divided iron is due to its extended surface in relation to its mass and it has been found that other forms of iron having an extended surface, for instance spongy iron produced by reduction of iron compounds, may be used successfully.

By using such finely divided iron or other form of iron having an extended surface in relation to its mass not only does the quanitty of iron necessary for the reduction approximate much more closely to that required theoretically than is the case where iron turnings are employed, but the caustic alkali such as caustic soda commonly employed in alkaline reductions may frequently without detriment be replaced wholly or in part by alkaline earth oxides or. hydroxides, for example lime.

, As has been indicated the iron employed should be as finely divided or have as extended a surface as possible, and may be: of such a degree of subdivision as to be pyrophoric. Thus for example iron prepared by the reduction of precipitated ironhydroxide why the reduction of iron oxide prepared by the action of heat on the nitrate is eminently suitable for use in accordance with the present invention. A further convenient method for the preparation of iron suitable forthe use in accordance with"the'present inventionis by the decompositionof iron carbonyl, e. g. by the action of heat on iron" carbonyl. Methods in whichfthe iron is produced from compounds erally unnecessary particularly where pyrophoricv iron is employed.

, As an alternative the. iron carbonyl may actuallybe decomposed in situ the iron being thus produced in a finely divided form actually in reduction mixture.

The reduction of nitro compounds may be carried out at elevated temperatures, for example at 90--l00 C.', and preferably is carried out in the absence of oxygen. Itis preferred therefore to carry out reduction in a neutral or reducing atmosphere, for example in an atmosphere of hydrogen or nitrogen.

If necessary or desirable the reaction may be regulated by the addition of diluents, for example hydrocarbons or alcohol, to the reduction mixture, but in general such additions have not been found to be essential.

While the invention has been described more particularly in connection with the production of hydrazobenzene by the reduction of nitrobenzene, other hydrazo compounds may be prepared by the reduction of the corresponding nitro compounds. Thus for example nitro-toluenes, nitroanisoles and nitro-xylenes may be reduced by the process of the present invention. The invention furthermore is not limited to the production of hydrazo compounds, but is applicable to the production of amino, azo, or azoxy compounds by the reduction of nitrocompounds, and to the reduction of nitrogen containing and other organic compounds capable of reduction in general.

In the production of benzidine and substituted benzidines, the hydrazo compound is if necessary isolated, and then treated with acid, when conbenzidine'being soluble in the hot liquor.

version to the benzidine compound takes place.

Thus for example in the production of benzidine from hydrazobenzene,the hydrazobenzenemay be treated with hydrochloric acid, preferably Without heating, when an almost quantitative con- Version is obtained. Where derivatives such as the acetyl or benzoyl derivatives of benzidine are required these may be obtained directly by heating the hydrazo compound with the organic acid or anhydride or with a mixture of the acid and anhydride. Thus for example acetyl benzidine may be obtained by boiling hydrazobenzene with acetic acid.

The following example illustrates the invention without being in any way limitative:--

Example 100 parts of nitrobenzene are stirred with 50 parts of very divided iron obtained by reducing iron oxide with hydrogen or by thermal decomposition of iron carbonyl, in a vessel containing an atmosphere of nitrogen and are then heated to about 90 C. when 80 parts of 60% caustic soda are gradually added, the temperature being maintained at about 100 C. The mixture is well stirred and when the formation of azoxybenzene is complete as shown by the setting point of the mixture, a paste of 16 parts of iron and 40 parts of 60% caustic soda is added. The mixture is stirred at the same temperature until formation of azobenzene is complete.

A further 16 parts of iron and 40 parts of caustic soda are then added, the mass being maintained in a liquid state by raising the temperature towards the close of the reaction to about 130 C. When reduction is complete the crude hydrazobenzene is separated from the iron oxide and caustic alkali. To convert it into benzidine it is stirred for several hours in the cold with hydrochloric acid of 24 B. and the mass then heated to 80 C. the The hot solution is then filtered and the benzidine precipitated as the sulphate by the addition of sulphuric acid. The benzidine sulphate is finally filtered off, washed and the base obtained in good yield by treatment with ammonia.

What I claim and desire to secure by Letters Patent is:-

1. Process for effecting reduction of a compound selected from the group consisting of nitro compounds and reducible reduction products of nitro compounds which comprises subjecting said compound to the reducing action of iron which has an extended surface in relation to its mass and which is prepared from compounds of iron by methods which avoid sintering or fusion of the metal.

2. Process for effecting reduction of a compound selected from the group consisting of nitro compounds and reducible reduction products of nitro compounds which comprises subjecting said compound to the reducing action of iron which has an extended surface in relation to its mass and which is prepared from compounds of iron by heating the same at a low temperature whereby sintering or fusion of the metal is avoided.

3. Process for efiecting reduction of a compound selected from the group consisting of nitro compounds and reducible reduction products of nitro compounds which comprises subjecting said compound to the reducing action of pyrophoric lIOIl.

4. Process for effecting reduction of aromatic nitro compounds which comprises subjecting said compounds in alkaline media to the reducing action of iron which has an extended surface in relation to its mass and which is prepared from compounds of iron by methods which avoid sintering or fusion of the metal.

5. Process for effecting reduction of aromatic nitro compounds which comprises subjecting said compounds in alkaline media to the reducing action of iron which has an extended surface in relation to its mass and which is prepared from compounds of iron by heating the same at a low temperature whereby sintering or fusion of the metal is avoided.

6. Process for the production of hydrazo benzene which comprises reducing nitrobenzene, in alkaline media with iron having an extended surface in relation to its mass and which is prepared from compounds of iron by methods which avoid sintering or fusion of the metal.

7. Process for the production of hydrazo benzene which comprises reducing nitrobenzene, in alkaline media with iron having an extended surface in relation to its mass and which is pret pared from compounds of iron by heating the \same at a low temperature whereby sintering or fusion of the metal is avoided.

8. Process for the production of hydrazo benzene which comprises reducing nitrobenzene, in alkaline media with pyrophoric iron.

HENRY DREYFUS. 

